Ankle fractures

Introduction

Ankle fractures are among the most common fractures treated by physicians and are comprised of a range of different injury patterns and vary in severity. Isolated malleolar fractures make up approximately two thirds of ankle fracures with bimalleolar fractures occurring in one-fourth and trimalleolar fractures occurring in the remaining 7% of cases. Open fractures are rare, occurring approximately 2% of the time. The overall incidence of ankle fractures has dramatically increased over the last 50 years and currently the highest incidence is seen among elderly women. The risk of ankle fracture is increased by smoking and high body-mass index.

Anatomy

The ankle joint or talocrural joint is formed by contributions from the tibia, fibula and talus. When the foot is dorsiflexed, the widened anterior portion of the talus fits securely within the medial and lateral malleoli and the talocrural joints acts as a true mortise with the boney structures providing the majority of the stability. As the ankle moves into plantarflexion, the narrower portion of the talar dome articulates between the medial and lateral malleoli. In this position the talus does not fit as securely and the majority of the joint stability is conferred by surrounding ligaments.

The ankle is often thought of as a simple hinge joint. However, biomechanically, the axis of rotation is constantly changing as the ankle allows variable degrees of rotation and translation in the coronal and axial planes as well as the sagittal plane.

Classification

A number of methods of classification exist for ankle fractures. A common method used to convey information regarding an ankle fracture is to simply describe the fracture. Important aspects to describe include whether the fracture is open or closed, the condition of the soft tissue (i.e. swelling, blisters) and the boney structures involved (i.e. bimalleolar, trimalleolar.) Additional points may include the fracture pattern, amount of comminution and the status of the syndesmosis.

An additional method of classification is simply to describe a fracture as stable or unstable. Stable fractures are those that have no displacement and are able to withstand physiologic forces. Signs of an unstable fracture include: medial or posterior malleolar fractures, medial clear space widening or tibiofibular disruption. This classification method can suggest the treatment method, as unstable fractures often require stabilization. A radiologic stress examination may be required to determine if a non-displaced fracture of the fibula is an isolated lateral injury or is associated with syndesmotic or medial sided injury. Physical examination revealing medial tenderness has been shown to have poor positive predictive value for significant deltoid injury (Tornetta et al). In this case a radiograph taken with an external rotation stress applied (via gravity or manual pressure) may reveal an increased medial clear space suggesting occult instability and may push one towards operative fixation (consider moving this discussion to later in article).

More systematized methods include the commonly used Lauge-Hansen Classification, the Weber classification and the OTA classification. The Lauge-Hansen classification is based on the fracture patterns observed from a series experiments by Lauge-Hansen in which cadaveric ankles were placed in either supination or pronation and loaded to failure by either a translational or rotational force. Rotational forces were external rotation, while translational forces were either adduction or abduction. These experiments yielded four fracture patterns. The fracture patterns are named first by the position of the foot and secondly by the direction of rotation or translation applied to create the fracture. In the L-H system, the injury starts at the tension side of the ankle and proceeds in the direction of the applied force. Strengths of this system include assistance in understanding the fracture forces that need to be counteracted for proper reduction and neutralized by surgical fixation Weaknesses of this system include poor interobserver and intraobserver reliability and lack of association with treatment suggestions.

The most common mechanism is the supination external rotation (SER) pattern. There are four designations of this fracture pattern numbered 1-4. The designations describe the sequential failure of anatomic structures as the external rotation force progresses. SER 1 describes failure of the anterior talofibular ligament (essentially an ankle sprain). SER 2 describes a fracture of the fibula tipically a posterolateral distal fragment with the anteromedial fracture line at the level of the plafond. SER 3 is failure of the posterior inferior tibiofibular ligament or a posterior malleolur fracture (Volkman's fracture). Finally, SER 4 describes a medial malleolus fracture or deltoid ligament rupture.

Another pattern of failure observed was the supination-adduction (SAD) pattern. SAD 1 injuries involve a fracture of the lateral malleolus at the level of the joint line or more distal (typically transverse). Supination-adduction 2 injuries have an additional vertical fracture of the medial malleolus.

Pronation-external rotation (PER) injuries fail initially on the medial side. PER 1 injuries begin with a fracture of the medial malleolus. PER 2 injuries involve a failure of the anterior tibiofibular ligament. PER 3 injuries demonstrate a high oblique or spiral fibula fracture beginning above the level of the joint. PER 4 fractures add an injury to the posterior tibiofibular ligament or posterior malleolus fracture.

Pronation-abduction injuries begin with a fracture of the medial malleolus or rupture of the deltoid ligament. This is followed by a failure of the anterior tibiofibular ligament. Progressive force leads to a high (above the joint line) comminuted fracture of the fibula.

The Weber classification was initially a simple classification scheme that was designed to easily categorize fractures; the assumption in the original classification was that lateral (fibular) stability was critical to ankle stability. The Weber scheme is divided into three categories based on the level of the fibula fracture in relation to the joint line. Weber A fractures occur distal to the joint line, while Weber B fractures involve the joint line and finally, Weber C fractures are confined above the joint line. It was felt that Weber A fractures could be treated non-operatively, Weber B fractures required stabilization of the fibula and Weber C fractures required syndesmotic stabilization in addition to fixation of the fibula. However, it is currently believed that medial stability contributes significantly to ankle stability and must be considered in the treatment decision. Agreement reliability is good for this classification because it is simple but because of this, it lack a robustness of information that the L-H system provides.

The AO/OTA classification is an extension of the Weber classification and is quite comprehensive. It uses an alphanumeric system to classify fractures and has three types, nine groups and 27 sub groups. The types A, B, and C were retained from the Weber classification.

Clinical Presentation

Ankle fractures usually are the result of low energy torsional forces and typically present with swelling, deformity and inability to bear weight. However, non-displaced ankle fracture presenting early after injury may exhibit minimal swelling and no deformity.

On examination, it is important to fully inspect the ankle for an open wound and the condition of the skin. A complete neurovascular exam should follow and should be repeated after reduction maneuvers. The tibia, fibula and midfoot should be palpated for tenderness. Compression of the tibia and fibula, the so-called squeeze test, should also be performed as this may be a sign of syndesmotic injury. This test is performed by compressing the tibia and fibula together proximally and eliciting pain at the syndesmosis.

Ottawa Ankle Rules
The Ottawa Ankle Rules were designed to aid health care professionals, especially emergency room and primary care physicians in determining among those patients presenting with ankle pain, the ones that were likely to have a fracture and thus warranted the added expense of radiological evaluation. A nearly 100% sensitivity for predicting fracture was found when one had pain near a malleolus and one or more of the following was fulfilled 1) age > 55, 2) inability to bear weight 3) tenderness at the tip of the malleolus. In this situation, radiographs are indicated.

Imaging

Three views (AP, lataral and mortise) should be obtained and evaluated for fracture and talar subluxation or dislocation. Evaluation of the talocrural angle, medial clear space and tibiofibular clear space will aid in determining proper alignment. The talocrural angle is the angle subtended by a line drawn parallel to the articular surface of the plafond and one connecting the tips of the malleoli. The angle is normally 4 to 11 degrees. The medial clear space is the distance from the lateral border of the medial malleolus and the medial border of the talus and should be equal to the superior clear space. A distance greater than 4mm or greater than the superior clear space is a sign of lateral talar subluxation. The syndesmosis can be evaluated radiographically by measuring the distance between the medial wall of the fibula and the incisural surface of the tibia on both the AP and mortise views. A clear space greater than 6mm on either view indicates injury to the syndesmosis.

Treatment

Initial management should consist of reduction of any dislocation. The goal is to reduce the talus underneath the tibial plafond to minimize the amount of abnormal soft tissue pressure which can lead to pressure ischemia. Understanding the deforming forces (i.e. L-H Classification) may aid in reduction by manual reversal of those forces. Failure to adequately reduce the talus is an indication for urgent open reduction and may be due to interposition of soft tissue or boney fragments. Any open injuries should be cleared of gross debris and covered with a sterile dressing and appropriate prophylactic antibiotics should be administered. The ankle should be immobilized in a well padded splint and the extremity elevated to minimize soft tissue swelling.

After initial evaluation and stabilization, the decision for definitive management should be made. Biomechanical and clinical information indicates that restoring and maintaining the talus centered and reduced beneath the plafond is one of the most important predictors for successful outcome. For fractures that are non-displaced or demonstrated to be stable on radiographic stress examination, definitive management consisting of ankle support (short leg cast, CAM walker, air cast) a brief period of protected weight bearing and crutches has lead to excellent functional results. Initially, frequent radiographs to evaluate for subsequent displacement are indicated. For fractures that are displaced, but an anatomic reduction is achieved, these fractures may be treated in a long leg cast with frequent radiographic assessment.

For displaced or unstable fractures, operative fixation is often indicated. It has been shown that even a 1mm lateral talar shift results in a 42% increase in contact loading of the tibiotalar joint, which may lead to early post traumatic arthritis. However, limited long term outcomes on isolated lateral maleolar fractures suggest good outcomes for non-operative treatment.

The timing of surgery is important. With the limited soft tissue around the ankle, careful attention should be paid concerning the swelling and soft tissue injury prior to planning operative fixation. The wrinkle test, in which the skin shows signs of wrinkling, indicates that soft tissue edema has resolved to an extent that soft tissue complications will be reduced. Blood filled blisters indicate injury to the dermis and should be allowed to resolve prior to planning an incision through them. Grossly unstable high energy fractures or high grade open fractures may be best treated with a two staged protocol in which the length, alignment and rotation are initially maintained with external fixation. Definitive internal fixation is then performed when the soft tissue or wounds are improved and free of infection.

There have been many methods described for fibular fixation. Traditional fixation consisted of a lateral approach followed by direct manual reduction, placement of a lag screw and lateral neutralization plating. Recent locking plate technology may provide stronger fixation and allow for bridge plating in severely comminuted fractures. In SER injuries, posterlateral plating has the advantage of counteracting the fracture deformation forces and posterior to anterior distal screw placement (taking advantage of the longer AP diameter and the stronger bone on the posterior surface). Posterior antiglide plating (using the plate to assist in fracture reduction) may be employed for oblique fractures that displace posteriorly. Long oblique fractures in a stable ankle may be amenable to lag screw fixation only. Intramedullary rods and k-wires have also been used as primary or supplemental fixation for more proximal injuries.

Transverse medial malleolus fractures are often stabilized with one or two screws in a lag fashion. Tension banding with Kirschner wires (or tensioned plate and screw constructs) can be employed for small fracture fragments. For vertical fractures of the supination-adduction type, a medial antiglide plate or transverse lag screw placement is effective.

The posterior malleolus often is effectively reduced when the fibula is stabilized. Indications for operative fixation include greater than 25-30% involvement of the plafond or greater than 2mm step off. The posterior malleolus may be stabilized with lag screws from an anterior or posterior direction or with a posteriorly placed buttress plate.

Sydesmotic injury is often diagnosed on radiographs. However, the sydesmosis should be evaluated fluoroscopically at the time of fixation. This can be achieved after both the medial and lateral maleoli stabilized by the Cotton test (manual/clamp distraction of the fibula away from the tibia, classically, by 1 cm) or an external rotation test. Recognition of syndesmotic injury is important as sydesmotic instability may lead to talar subluxation and arthritis.

Stabilization of the syndesmosis should begin with anatomic reduction. Careful attention should be paid to fibular length and rotation. The syndesmosis may be stabilized via a number of methods and techniques and the optimal method of fixation remains controversial. Two screws are more stable than one screw and 3.5mm and 4.5 mm screws perform similarly. A fully threaded screw placed from the fibula to the tibia engaging either 3 or 4 cortices can stabilize the syndesmosis. Some authors prefer 3 cortices as this theoretically allows some motion at the syndesmosis, which is thought to be more physiologic. Larger screws placed over 4 cortices are easier to remove, especially when broken. Additionally, the screw breakage rate is lower when 3 cortices are engaged. However, some authors prefer the increased rigidity of four cortices. The timing of weight bearing and whether to remove the screw prior to allowing weight bearing is controversial. Broken syndesmotic screws are relatively rare and usually asymptomatic. Newer methods of syndesmotic fixation include suture fixation that may allow physiologic motion. Dorsiflexion of the ankle during syndesmotic fixation has not been shown to be important in determining ankle function.

Ankle Arthritis - Usually occurs within 2 years of injury. More common in severely displaced fractures, bimalleolar fractures and those involving the posterior malleolus.

Broken hardware

Red Flags and Controversies

Surgical indications continue to be controversial especially in regards to the requirement of surgical stabilization of stable lateral mallolar fracture and posterior malleolar fractures.

Nearly all aspects of syndesmotic fixation are controversial including the size and number of screws, the number of cortices engaged, the timing of weight bearing and whether to remove or retain syndesmotic screws. See above.

Outcomes

Most patients can expect good results after rotational ankle fractures. Stable ankle fractures treated non-operatively have consistently demonstrated excellent results. Operative fixation of unstable fractures has also produced good results in over 85% of cases. Results seem to improve with more accurate reduction. Factors found to negatively impact the ability to achieve a satisfactory outcome include, involvement of the posterior malleolus, impaction of the talus, fractures in diabetics and severe dislocation of the talus. Mild to moderate symptoms may persist for years after radiographic fracture healing.

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